The music/sound speed of the OKI6295 in Steel Force is too slow.
I found an arcade video of the game and compare the music at time=1:08s with the one in MAME.
The OKI6295 speed in MAME is 937500 Hz, that's the board cyrstal divided by 16 (15Mhz / 16 = 937500 Hz)
A factor of 14 is exactly the speed in the video.